The White House Thursday said North Korea’s plan to conduct a third nuclear test is “needlessly provocative” and will only increase Pyongyang’s isolation.

Spokesman Jay Carney’s comments were in response to the North’s National Defense Commission, which also made clear Thursday that its long-range rockets are designed to carry warheads aimed at striking the United States. The North has previously said its launches are for a peaceful space program.

Pyongyang’s statement came two days after the U.N. Security Council condemned its December launch of a satellite atop a long-range rocket for violating a ban on ballistic missile activity. The council, with the support of the North’s only major ally, China, also tightened sanctions.

“North Korea’s statement is needlessly provocative and a test would be a significant violation of United Nations Security Council resolutions,” Carney told reporters. “Further provocation would only increase Pyongyang’s isolation, and its continued focus on its nuclear and missile program is doing nothing to help the North Korean people.”

Carney said the council decision to tighten sanctions would impede the growth of weapons of mass destruction programs in North Korea. He said the U.S. would be taking steps, but did not specify them.

He also noted the council’s warning to take further action in the event of a further launch or nuclear test.

“We judge North Korea by its actions, and provocations like these are significant violations and we act accordingly,” Carney said.

North Korea conducted nuclear tests in 2006 and 2009. It claims the right to build nuclear weapons as a defense against the United States, its foe from the 1950-53 Korean War. The U.S. still maintains 28,000 troops in South Korea as a deterrent against aggression from the North.

North Korea’s recently launched rocket has the potential to hit the west coast of the U.S. mainland, but experts say it still doesn’t have the capability to make a missile re-enter the atmosphere and hit a target. Nor is it believed to have miniaturized a nuclear device to mount on a missile. A nuclear test could move it closer toward that goal.

The elevation a year ago of Kim Jong Un as North Korea’s new leader had fueled hope of improved relations with Washington, particularly after the North accepted a substantial offer of food aid in exchange for nuclear concessions. But that agreement collapsed last April when the North conducted a long-range rocket launch.

Carney said the U.S. has not seen a noticeable change in North Korea’s behavior.